Forecasting frost

Frost

Frost can be challenging to forecast due to all the different weather conditions - such as cloud cover and air temperature - which can influence the formation of frost.

Forecasting air temperature and frost more than a few days in advance can be complex due to many weather variables that need to be taken into account. Cloud cover, which is one of the more challenging variables to forecast accurately at longer forecast lead times, can have a big influence on surface air temperature and hence the formation of frost.

The minimum air temperature will provide a good basis for frost and ice risk in your location. However, it is important to note that in some situations a ground frost can form even when the air temperature is above 0 °C. This is because of a process known as radiative cooling, whereby the ground, trees and objects cool faster than the surrounding air. This situation is most common during a long winter night when skies are clear.

Frosts usually occur during winter nights when energy from the sun is not available to heat the surface. On cloudy nights, cloud can act as a 'blanket' and trap warm air near the surface meaning frost formation is unlikely. On the other hand, clear nights allow any surface warmth to rapidly radiate out into the atmosphere cooling the surface and leading to frost formation. Other weather variables which influence surface air temperature and the formation of frost include wind speed and rainfall.

Due to the chaotic nature of the atmosphere, the maximum and minimum temperature ranges for each day are generated by running a range of weather models - this technique is known as ensemble forecasting. The maximum and minimum temperatures for the next five days are extracted from each weather model to produce a range of possible maximum and minimum temperature scenarios.

Last updated: 25 October 2013

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